Electric heater unit and method of making same



Sept. 3, 1935. H. E. TRENT Er AL 2,012,977

ELECTRIC HEATER UNIT AND METHOD OF MAKING SAIE Filed March 24, 1952 2 sheets-sheet 1 iwf-22A :werden 5 la Ero/dlffrem* d Char/6,511'. FWzlngy.

Sept. 3, 1935. H. E. TRENT ET Al. 2,012,977

ELECTRIC HEATER UNIT AND METHOD OF MAKING SAME Filed March 24, 1932 2 Sheets-Sheet 2 Patentedsept3,l935

UNITED STATES PATENT VoFr-'lcE um() mm UNIT AND m01) l' m6 8m llanldllraltallcharleela'hitncmfhlh.

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8 Ohh. (CI. ICI-81) tion of the sheathing, but also to the fact that the insulation material between the resistor and the sheathing is either of cementitious material or is artincially compacted or compressed upon or after assembly. An object of this invention therefore is to provide a heater in which the replacement of the resistor is readily accomplished (preferably upon return to the factory) so that the heater possesses a distinct salvage value.

Another object is to provide an improved method of making a strip heater, which broadly consists in forming a sheathing by compressing an original tube until it has two substantially parallel sides, removing a portion of one of said sides adjacent to one end to provide for a terminal block, closing and sealing the opposite end, inserting into the sheathing either a straight or a coiled resistor element threaded through apertured beads, which when within said sheathing extend in two or more preferably spaced parallel rows, then preferably inserting by gravity dry finely divided powder to illl the slight spaces or void between said beads and said sheathing, securing said terminal block in operative position as by bringing together the opposite sides of said sheathing at the end adiacent to said block, and then, if desired, by rolling or otherwise pressing a groove into one or both sides of said sheathing between and operative to space apart adjacent rows of said beads, the ends of said resistor having been connected to terminals carried by said block.

A further object is to provide a strip heater which is adapted to be bent, curved, warped, or flexed, within certain limits, this being made possible by the resistor extending through beads. which are somewhat smaller than the inside width of the sheathing, and when such bend or the like is effected, the sides of said beads extend as cords across the curved interior of the sheathing. In addition, the dry, heat-conducting powder surrounding said beads within said sheathing serves both to fill the space or void surrounding said beads and in the cracks between them. and also serves as a cushion between beads and sheathing, with the result that impaired insulation due to chipping and breakage of the beads is not known. The use of powder furthermore makes it possible to again straighten or otherwise alter the shape of a curved strip heater as for the purpose of withdrawing and replacing a burned out resistor, whereas strip heaters in which cementitious material is used cannot be bent or straightened after such material has once set.

With these and other objects in mind. the present invention comprises further details of construction and operation, which are fully brought out in the following description, when read in conjunction with the accompanying drawings in which Fig. l is a perspective view of a tube as the first step in the process of making the improved heater; Fig. 2 is a similar view showing the tube flattened and a portion of one side of the same removed; Fig. 3 is a longitudinal vertical section of the heater on the line 3 3 of Fig. after the beads, resistor and terminal block have been inserted and the central groove formed; Fig. 4 is a side elevation of the same partly in section along the line L-l of Fig. 5 and after the block-positioning member has been inserted and the end of the tube compressed to prevent movement of the several elements within and from the sheathing; Fig. 5 is a top plan view of the device after having been completely formed; Fig. 6 is a perspective view of the terminal block per se; Fig. 7 is a similar view of the block-positioning member per se; Fig. 8 is a horizontal section on the line l-l of Fig. 4; Fig. 9 is a transverse section of the heater before the groove is pressed in the same; Fig. 10 is a similar view but taken on the line III-il of Fig. 5, and showing the groove in the sheathing; Fig. il is a vertical section on the line iI-II of Fig. 5; Fig. 12 is a longitudinal section through a modified form of heater; Fig. i3 is a transverse section on the line IS-II of Fig. l2; Fig. i4 is a schematic view, showing the beads and resistor of the modiilcation laid out in developed view to better show their relationship; and Fig. 15 is a fragmentary perspective view of a slightly modified form.

Referring to Figs. l to ll of the drawings, the method of forming the improved heater comprises flrst the cutting to proper length of a tube I, which is then flattened to substantially the shape shown in Fig. 2, thus providing upper and lower plannular walls 2 and 3, connected by curved side portions l. 'Ihis flattened tube is Cil then closed at one end l as by curving and welding, while the opposite end portion of the upper side wall is provided with a rectangular cutout region bounded by an inner end edge I and lateral side edges l.

The resistor may comprise a rectilinear wire or the like, but is here shown as embodying a spirally formed wire t, which is threaded through preferably parallel series of beads I made of glass, clay, porcelain, or similar insulating msterial. each bead being transversely elongated and preferably provided with two or more apertures I0. Within the type of strip heater shown in Figs. 5 and 8, there is space for two series of such beads with a space between the seri, affording four rows of aligned apertures, so that the resistor element can pass lengthwise through one outside aperture row, reversely through a central row, reversely in the first direction through the other central row, and then reversely again through the other outside row, those portions of the resistor between the respective outside and adjacent inside aperture rows extending through beads having transversely exending connecting channels Il, which serve to effectively protect such portions of the resistor from possible contact with the adjacent closed end of the sheathing.

In Figs. 3 to 6 and 8, a terminal block of suitable insulating material is shown, the same comprising a body section l2 from the lower portion of which laterally extends a peripheral flange comprising a forward portion I3, side portions il and a rear portion I5. This block is adapted to be inserted in the open end of the sheathing as shown in Fig. 2, with the body section positioned between the sheathing edges 1 and against the edge 6, while the forward flange portion extends beneath the edge 6 and the lateral flange portions extend beneath the edges 1 and are seated within the curved sides 4 of the sheathing. 'I'he forward portion I3 of said block is provided with an arcuate recess I6 for the reception of that part of the resistor Il, which connects those portions extending through the central rows of bead apertures, while upon the opposite sides of said recess said block is provided with inwardly and convergingly extending channels Il and I9, which lead toward and communicate with upwardly extending bores 20 and 2|, in which are secured suitable binding posts 20* and 2I, to which the ends of the resistor element are secured.

After the resistor element has been threaded through the beads and the latter have been arranged within the sheathing, the spaces around and in certain instances between said beads, and between the rows of beads, are filled with finely divided powdered material 9*, possessing the characteristics of heat conductivity and electrical resistivity. Heretofore, it has been customary to employ for this purpose various forms of ceinentitious material which sets into a solid mass, or when filling the void with granulated material to subsequently compress this material artificially into a compacted mass, which is for practical purposes substantially as permanent as the former. In the present device, the powder is finely divided in th-e first place, and is then thoroughly dried so that it will flow with the utmost freedom. At no time is it compacted, for its cushioning function between the beads and between the beads and sheathing would be thereby destroyed or greatly decreased. Furthermore, in the form of dry unpacked powder the filling material permits the unit to be bent or curved Wimin certain limitations defined only by the relationship of the sise and shape of the beads to the sheathing. However, if it is felt that the mene flowing of the powder into the device fails to enter the entire space surrounding the beads and the interstices between them. the sheathing may be vibrated, Joggled, or tapped, so as to accelerate the flow of the powder, but no greater packing of the same being desired than that made possible by gravity.

After the resistor, beads and terminal block have been operatively positioned and the powder inserted as above described, the positioning member shown in Pig. 7 is inserted in the open end of the sheathing, as shown in Figs. 3, 4, 5 and 8. This member comprises a sheet metal structure formed of a flat base portion 22, normally resting upon the lower wall I of the sheathing, an upwardly extending portion 2l, and a second horizontally extending portion 24, which normally rests upon the rear portion Il of the terminal block flange, the free edge 2l of said member bearing firmly against the restricted upwardly extending portion of the body of said block. With said member in that position, the rearward end portions 2l of the overhanging flanges 'I are pressed downwardly towards the bottom wall I of the sheathing, so as to bind therebetween the base portion 22 of the block-positioning member. One or more apertures 21 may then be placed in the adjacent elements comprising said last-mentioned sheathing wall and said member, as shown in Figs. 4, 5 and 8, for operatively securing the heater by bolts or the like to a suitable support (not shown). The binding posts 2lil and 2 I* may then be electrically connected to a suitable source of electric current and to any desired form of current regulating means. Finally, after the heater unit has been assembled as thus described, one or more grooves 28 are formed in the sheathing as indicated in Figs. 3 and 10, such groove or grooves being created either by means of suitable dies, or by means of a roller which is preferred, as it is capable of operating upon any length of unit without alteration. Instead of the single groove, a pair of oppositely positioned grooves may be employed, the function of such groove or grooves being to so shape the sheathing that it effectually separates adjacent rows of beads, and makes the beads of each row maintain a predetermined alignment. Obviously, too, such groove may be pressed in the sheathing before the insertion of the beads therein if desired, and if formed after the insertion of the beads it may be created either before or after the injection oi' the powder, though it is preferable that it be so formed before such powder insertion, as otherwise the powder is compressed to an undesirable degree by the pressure of the die or roller.

Referring now to Figs. i2 to 13, a slightly modified type of heater element is sliown as comprising a hollow, substantially rectangular sheathing 30, one end of which is closed at 3|, while at least two of the opposite side walls may be provided with grooves 32 to effectually separate oppositely positioned rows of beads 32, each bead having two or more spaced apertures 34 through which extend a preferably spirally coiled resistor element 35. The arrangement of said element through the consecutive beads in each row and through the beads of the separated rows is diagrammatically shown in Fig. 14. 'Ihose portions 36 of the resistor extending between the apertures in a given series of beads are protected from contact with the inner closed end of the sheathing by individual beads 31, while the free ends 38 and an intermediate portion 39 of said resistor may be connected to any suitable form of binding posts 40, carried by a block 4l of insulating material and serving if desired as a closure for the-otherwise open end of the sheathing, said closure block being maintained in operative position by any suitable means as for instance the inturned or crimped edge portion l2.

Referring to Fig. 15, there is shown a form of the device which is in many ways similar to the form ilrst described, and so like parts have the same numerals. However, the block-retaining member shown in Fig. 7 is omitted, and in lieu thereof a plate 45 is laid in the open end of the casing and spot-welded at one or more points 46, in order to fixedly position the inner edge portion 41 of said member against the near end portion of the block I2. This simplified form of retaining means may be turned upwardly at its laterally opposite edge portions 4B in order to conform to the similarly curved adjacent portions of the casing and operatively position it while being welded, and both said casing and said member may then be provided with aligned apertures Il for the insertion of a suitable supporting bolt or other desired element (not shown). A distinct advantage of this construction lies in its salvage value, due to the fact that, whenever a resistance element burns out, the device may be returned to the factory, the retaining member pried free from the casing, the parts of the device removed and new elements where needed inserted, and the same or another retaining member secured in position as before.

Having thus'described our invention, what we claim and desire to protect by Letters Patent of the United States isz- 1. A heater comprising a sheathing, a plurality of rows of bored members of insulating material within said sheathing, the members of the respective rows being in end to end contact, an electric resistor element extending through the bores in said members, an extension on said sheathing projecting between and operative to maintain adjacent rows of said members in predetermined spaced relation, and fluent insulation in said sheathing jointly with said members substantially filling said sheathing.

2. A heater, comprising a sheathing, a plurality of rows of beads within said sheathing, each bead having a plurality of bores, and the beads of each row being in end to end contact and having their corresponding bores in alignment and having a resistor element through them, said sheathing extending transversely inwardly between and operative to maintain said rows of beads in spaced relation, and powdered material having heat-conductive and electrically-insulating characteristics, said beads and powdered material jointly substantially filling said sheathing.

3. A heater, comprising a tubular sheathing closed at one end, a terminal block positioned in and beingexposed thru an aperture in the sheathing in spaced relation with the closed end. a resistor element extending through said sheathing and having its terminals operatively connected to said block, bored beads in end to end contact through which the resistor element passes, and a positioning member within the end portion of said sheathing adjacent to and cooperating with said block, and said sheathing being compressed upon and thereby operative to secure said member in fixed position to secure said block against shifting and to provide a reinforced supporting portion for said heater, a wall of said sheathing being corrugated and extending transversely inwardly between said rows of beads whereby said wall is stiffened, and fluent insulating material in the sheathing jointly with said beads substantially lling the sheathing.

4. The method of making a heater, which consists in threading a resistor element through a plurality of sets of insulating beads, securing the ends of said resistor to a terminal block, inserting said beads in end to end contact, resistor and block into a sheathing, inserting a fluent insulating material into the sheathing in a quantity to substantially ll the sheathing jointly with said beads, and then collapsing the entrance end portion of the sheathing in alignment with the path of entrance of said block, to secure the block in fixed position and prevent the accidental loosening and removal of the beads and resistor.

5. The method of making a heater, which consists in threading a resistor element through a plurality of sets of insulating beads, securing the ends of said resistor to a terminal block, inserting said beads in end to end contact, resistor and block into a sheathing, inserting a uent insulating material into the sheathing in a quantity to substantially li the sheathing jointly with said beads, inserting a positioning member in said sheathing to the rear of said block then compressing the entrance end portion of the sheathing upon said member and in alignment with the path of entrance of said block, to secure the block in fixed position and prevent the accidental loosening and removal of the `beads and resistor, and then pressing a portion of a wall of the sheathing inwardly to prevent transverse movement of said beads.

6. A heater having a hollow sheathing closed at its opposite ends, beads of insulation in the space of the sheathing in end to end contact, said beads having bores, a resistor disposed in said bores, and uent insulation in said space about the beads and jointly with said beads substantially lling said space.

'1. The method of making an enclosed and armored resistor, which consists in forming a resistor conductor, in assembling on said conductor preformed and calcined refractory insulators in sections completely covering the said conductor, thereafter inserting the completely covered resistor conductor into an armored casing, and filling the spaces in and around the resistor and insulators with a finely divided powder.

8. The method of making an enclosed and armored resistor. which consists in forming a resistor conductor, in assembling on said conductor preformed and calcined refractory insulators in sections completely covering the said conductor, thereafter inserting the completely covered resistor conductor into an armored casing. and filling the spaces in and around the resistor and insulators with a finely divided powder capable of remaining finely divided after heating.

' HAROLD E. TRENT.

CHARLES L. WHITNEY. 

